Lipoprotein lipase activity in the skeletal muscle during physical exercise in dogs

Effects of exercise training and feeding on lipoprotein lipase gene expression in adipose tissue, heart, and skeletal muscle of the rat

Lipoprotein lipase (LPL) is found in adipose tissue and muscle, and is important for the uptake of triglyceride-rich lipoproteins from plasma. This study examined the regulation of LPL in adipose tissue and muscle by exercise training in combination with the fed or fasted state. After training male rats on a treadmill for 6 weeks, LPL activity, mass, and mRNA levels were measured in adipose tissue, heart, soleus, and extensor digitorum longus (EDL) muscles and compared with levels in sedentary rats. Tissue LPL was measured as the heparin-released (HR) and cellular-extracted (EXT) fractions 16 hours following the last bout of exercise, during which time some animals were fasted and others were allowed free access to food. Training led to an increase in HR LPL activity and LPL protein mass in soleus and EDL, but had no effort on adipose tissue and heart LPL. The increase in soleus LPL with exercise was in the HR fraction only, whereas the increase in EDL LPL with training was in both the HR and EXT fractions. All these changes in LPL activity were accompanied by similar changes in LPL immunoreactive mass. However, there were no changes in LPL mRNA levels with training. Feeding induced a large increase in adipose tissue LPL activity and mass in both the HR and EXT fractions: however, there was no change in mRNA levels. In heart, feeding yielded a decrease in HR but no consistent change in EXT activity or mass, and a consistent decrease in mRNA levels. As compared with control rats, trained rats demonstrated different responses to feeding in all tissues, especially in soleus and EDL. Whereas feeding had no effect on LPL in soleus and EDL of control rats, feeding induced a decrease in HR and EXT LPL in the soleus of trained rats. In addition, feeding yielded a significant decrease in EXT LPL of the EDL of trained rats. Thus, these data demonstrate that adipose tissue and heart LPL are highly regulated by feeding and are not responsive to long-term exercise training. On the other hand, skeletal muscle LPL is increased in trained rats, but this increase is blunted considerably by feeding following the last bout of exercise. These changes in LPL activity and mass are mostly unaccompanied by changes in LPL mRNA levels, demonstrating that much physiologic regulation occurs posttranscriptionally.

Exercise-induced changes in lipoprotein lipase activity (LPLA) in skeletal muscles of the dog

The aim of this work was to study the effect of physical exercise on muscle lipoprotein lipase activity (LPL) in dogs. Existence of two forms of LPL: heparin releasable and unreleasable was demonstrated in skeletal muscles, and the changes in the activity of both forms were followed during 3 h treadmill running, using biopsy samples taken from m. biceps femoris. During the first two hours of exercise the heparin releasable form of LPL was progressively increasing, whereas the heparin unreleasable form of the enzyme was decreasing. Thus, a significant negative correlation between activities of the two forms was ascertained (r = 0.72, P less than 0.01). In the final period of exercise, activity of the heparin releasable form of LPL tended to stabilize on the enhanced level, and activity of the heparin unreleasable form increased. In the further series of experiments a relationship between exercise intensity and activity of the heparin releasable form of LPL was studied during 1 h exercise bouts. A significant positive correlation (r = 0.84, P less than 0.001) was ascertained between LPL activity and intensity of work. A comparison between LPL activity in the muscle engaged in exercise (m. biceps femoris) and nonactive muscle (m. coccygeus) revealed that the enhancement of the enzyme activity during physical work does not occur in the latter.

IN CONCLUSION

it was found that physical exercise induces a marked intensity-dependent increase of LPL activity in working muscles, which is probably caused by an elevated transport of the enzyme molecules from the muscle cells to the intravascular space. The latter suggestion is based on the reciprocal changes of the heparin releasable and unreleasable (probably intracellular) forms of LPL.

Metabolic and hormonal responses to prolonged physical exercise in dogs after a single fat-enriched meal

Metabolic and hormonal responses to prolonged treadmill exercise in dogs fed a fat-enriched meal 4 h prior to the exercise were compared to those measured 4 h after a mixed meal or in the postabsorptive state. Ingestion of the fat-enriched meal caused significant elevations in the resting values of plasma triglyceride (TG), free fatty acid (FFA), and glycerol concentrations. A reduction of the plasma TG concentration (from 1.6 +/- 0.2 to 1.1 +/- 0.10 mmol X l-1, P less than 0.005) occurred only in dogs exercising after the fat-enriched meal. No significant changes in this variable were noted in dogs fed a mixed meal, whilst in the postabsorptive state exercise caused an increase in the plasma TG level (from 0.42 +/- 0.03 to 0.99 +/- 0.11 mmol X l-1, P less than 0.01). The exercise-induced elevations in plasma FFA and glycerol concentrations were the highest in the dogs given the fat-enriched meal. Plasma glycerol during exercise correlated with the initial values of circulating TG (r = 0.73). The plasma FFA-glycerol ratio, at the end of exercise was lowest in the dogs taking the fat-enriched meal (1.39 +/- 0.19), suggesting an increased utilization of FFA in comparison with that in the postabsorptive state (3.27 +/- 0.37) or after a mixed meal (2.88 +/- 0.55). Basal serum insulin (IRI) concentrations were similarly enhanced in dogs fed fat-enriched and mixed meals, and they were reduced to control values within 60 min of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in muscle lipoprotein lipase activity during exercise in dogs fed on a mixed fat-rich meal

Skeletal muscle lipoprotein lipase activity LPLA was compared in dogs performing prolonged treadmill exercise after 20-22 h fasting or 4 h following mixed fat-rich meal ingestion. In the fasting state muscle LPLA increased progressively during 2 h exercise. In fed dogs the resting value of the muscle LPLA was considerably lower than that in the fasting state, and no increase in the enzyme activity occurred during physical effort. The inhibition of the muscle LPLA by the meal ingestion can be attributed to the persisting effects of increased plasma insulin and/or FFA concentrations, found at the beginning of exercise.

Influence of thyroid status on skeletal muscle LPL activity and TG uptake

The influence of thyroid status on the clearance of chylomicron 14C-labeled triglycerides (14C-TG), the fractional uptake of 14C-TG, and activity of lipoprotein lipase (LPL) in the different skeletal muscle fiber types was evaluated in pentobarbital-anesthetized rats. The turnover of plasma TG was approximately fourfold greater in the hyperthyroid (HyperT) compared to either euthyroid (EUT) or hypothyroid (HypoT) animals. The uptake of 14C-TG was increased in slow-twitch red and fast-twitch red muscle sections of the HyperT group and normal in the HypoT group. The changes in LPL activity in these two fiber types were inversely related to thyroid influence, with decreases found in the HyperT group and increases found in the HypoT group. Thus, the uptake of 14C-TG in these high-oxidative fibers, relative to the LPL activity, varied directly with thyroid influence. As a result, the normal linear relationship, apparent for the different types of skeletal muscle, between LPL activity measured in vitro and TG uptake determined in situ was not maintained.